A voltage-controlled oscillator (VCO) is a circuit that produces an oscillating signal using amplification, feedback and a resonant circuit to generate a repeating voltage waveform, such that its output frequency is proportional to its input voltage.
In wireless communication applications, VCOs operate over large frequency ranges. VCO's generally comprise a tank circuit and an amplifier circuit, operation of which will be well known. Biasing of such circuits is also known and described in U.S. Pat. No. 6,674,333 to Peckham et al, which describes a method for operating a band switchable VCO in different frequency bands. In typical band switching circuits, biasing of the amplifier or a tank circuit introduces noise which results in phase noise being present in the output of the VCO.
It is, therefore, desirable to provide a method and apparatus for reduced noise band switching circuits.